Hydrogen Bonding and Charge Transfer in Trifluoromethylated β-Aminoenones: A Combined Experimental and Theoretical Study

Abstract

Two new β-aminoenones, the NH-alkyl (2Z)-3-butylamino-4,4,4-trifluoro-1-(2-hydroxy-5-nitrophenyl)but-2-en-1-one (1) and its NH2 amino counterpart (2), were synthesized and characterized using experimental and theoretical methods. These closely related compounds differ only in their amino substitution. Spectroscopic data (IR, UV–Vis and NMR spectra) reveal characteristic bands and shifts associated with push–pull electronic distribution and support the planar conformation and tautomeric stability of the enaminone core. X-ray diffraction revealed nearly planar conformations stabilized by intramolecular O-H···O and N-H···O hydrogen bonds forming two six-membered pseudo-rings, while compound 2 also exhibits polymeric contacts associated with its primary amine functionality. Hirshfeld surface and interaction energy analyses indicated that electrostatic and dispersive forces dominate crystal packing, with enhanced van der Waals contributions in 1 due to the butyl chain. QTAIM and NBO analyses confirmed the resonance-assisted hydrogen bonding (RAHB) character of these interactions and elucidated key charge transfer pathways. The antioxidant activity evaluated by the DPPH assay complements the structural results, suggesting that the radical scavenging potential depends on the amino substituent. These results highlight the importance of push-pull effects in modulating molecular reactivity, supramolecular architecture, and potential bioactivity.